A group of prominent scientists and economists have issued a stark warning to the nation’s politicians: the Murray-Darling basin plan is failing to achieve environmental goals and is a “gross waste” of money.

The group of seven economists and five scientists with deep expertise in the river are meeting on Monday morning in Adelaide to issue what they are calling the Murray-Darling declaration.

It is an urgent warning to warn state and federal politicians that despite five years of effort, the Murray-Darling basin is not delivering environmental improvements for the basin as a whole.

They say while it’s possible to point to improvements in pockets of the river system the overall plan is a failure and has led to a massive waste of $4bn in taxpayer funds on projects that have failed to improve the great river’s health.

Prof Quentin Grafton, the director of the centre for water policy at the Crawford school at Australian National University and one of the signatories, said his personal concern was the “gross waste of taxpayers’ money”.

“This plan was designed to deliver public benefits. There are plenty of private benefits to irrigators – the value of their land is increased by these water projects –but almost no public benefits,” he said.

The group, which includes Prof John Quiggin, an economist from University of Queensland; Dr Richard Kingsford, one of Australia’s foremost experts on river wetlands and birdlife; and Prof John Williams, the former chief land and water scientist at CSIRO, are meeting in Adelaide to discuss how to bring their concerns to the attention of the nation’s politicians and to offer solutions.

“There is no time to waste,” the declaration says. “The basin remains in a poor state. While there have been improvements in specific sites, these have not resulted in measurable improvements in key environmental indicators at a basin scale.

“As of February 2018, some $4bn has been spent on water recovery infrastructure projects, but for many of these projects there is no scientific evidence that they have actually increased net stream flows, which was a key goal of water reform.”

For example, despite allocating half a billion dollars in 2007 to upgrade water meters in the basin, as much as 75% of all surface water diversions in the northern part of the basin may still not have water meters, the experts say.

The Wentworth Group warned that while the plan had good intentions, a lack of will by federal authorities and systematic undermining of elements of the plan by state governments and irrigators meant it was no longer effective.

Concern about the Murray-Darling plan came to the fore last year when the ABC’s Four Corners report into the Barwon-Darling catchment detailed startling allegations of water theft and the legal diversion of flows earmarked for the environment to irrigation under state-devised water sharing rules.

Since then an independent expert, Ken Matthews, has delivered a scathing report on the administration of water policy in New South Wales and a senior bureaucrat has been referred to the Independent Commission Against Corruption.

In 2016-17 there were no prosecutions for water offences in NSW and Queensland, and six in the other states.

The MDBA investigation concluded the MDBA, which has responsibility for the whole-of-basin outcomes, has not given sufficient attention to compliance, has not provided a clear statement of its compliance role, and has not dealt adequately with allegations of compliance breaches.

In the meantime, it is also proposing to cut the water recovery target for environmental water from in the northern part of the river by 70 gigalitres. The South Australian government is furious and has set up a royal commission.

“It’s time to fix the basin and tell the Australian public what is happening, and how to fix it,” Grafton said.

The signatories are calling for a halt to all publicly funded water recovery associated with irrigation infrastructure subsidies/grants in the Murray-Darling basin, until a comprehensive and independent audit of basin water recovery is published.

They also want to see a comprehensive and independent economic and scientific audit of all completed basin water recovery and a full scientific review, and an adequately funded, expert, scientific and independent body to monitor, measure and give advice about delivery of the Water Act.

“Unless the Australian and state governments fully deliver on the key objects of the Water Act (2007), the basin’s aquatic environments will remain impaired and billions of public money risks being spent without leading to the long-term sustainability of either irrigation or the environment and the support needed for key social-cultural values, they said.